The recording density of a magnetic recording/reproducing apparatus has been increasing at an annual rate from 40 to 60%, and is estimated to reach Tbit/in2 in the near future. Accordingly, it is required that a magnetic recording/reproducing head has higher output and higher resolving power. Presently, the magnetic reproducing heads such as a CPP-GMR (Current Perpendicular to Plane Giant Magneto Resistance) head in which a sense current is passed perpendicularly to the laminated plane, and a TMR (Tunneling Magneto Resistance) head, have been proposed. However, for these heads, it may be difficult to make the gap length Gw between shields 30 nm or less due to the requirements for the film thickness of an element, and difficult to apply them to the medium of 1 Tbit/in2 or more in respect of the resolving power. For example, the gap length of the reproducing head for the medium of 1 Tbit/in2 is Gw=25 nm, which can not be treated by the prior art such as the CPP-GMR or TMR.
Therefore, a high resolving power reproducing head using a spin accumulation effect has been proposed in “Spin Injection and Spin Accumulation in all-metal Mesoscopic Spin Valves”, F. J. Jedema et al., Physical Review B, vol. 67, (2003), p. 85319 (“non-patent document 1”), and Japanese Patent Publication No. 2004-342241 (“patent document 1”). The spin accumulation effect is a phenomenon in which when a current is passed from a ferromagnetic substance to a non-magnetic metal, spin polarized electrons are accumulated in the non-magnetic metal in the range of spin diffusion length λ. The spin diffusion length λ represents the distance where information of spin disappears (spin is reversed) and is a material inherent value.
Herein, a basic element (spin accumulation element) structure in which a non-magnetic metallic fine line is used as the non-magnetic substance and two magnetic substances are laminated on the non-magnetic fine line, will be described below. Of the two magnetic substances, the first magnetic substance is used as a spin injection source by passing a current from the first magnetic substance to the non-magnetic substance. The other or second magnetic substance is a detection part for the output voltage with spin accumulation effect. Since the ferromagnetic substance generally has a different spin density (the number of up spin electrons and the number of down spin electrons are different) at the Fermi level, a difference in the spin density is induced in the non-magnetic fine line by passing a current from the first magnetic substance to the non-magnetic substance. It is well known that due to the accumulated spin polarized electrons, the non-magnetic substance behaves like ferromagnetic substance in the range of spin diffusion length (see non-patent document 1 and “Spin Injection and Detection in Magnetic Nanostructures”, Physics Review B, vol. 67, (2003), p. 52409 “non-patent document 2”). Using this effect, a voltage difference ΔV is produced depending on the magnetization directions of the first magnetic substance and the second magnetic substance. This voltage difference is called an output voltage ΔV of the spin accumulation element. As a method for measuring the output voltage, a non-local voltage measurement in which no current flows through the voltage detection part is generally employed (see non-patent document 1). To increase ΔV, it is effective that the spin diffusion length λ is made longer, or the electrode distance d1 between two electrodes is decreased as disclosed in Japanese Patent Publication No. 2004-186274 (“patent document 2”).
The reproducing head using the basic element has a feature that a fixed layer and a free layer can be fully separated, and the gap length between shields can be narrowed down. However, the conventional spin accumulation element does not have enough output, and is required to have the higher output. One of the methods for increasing the output voltage of the reproducing head using the spin accumulation effect is to narrow down the magnetic substance interval d1 between two magnetic substances making up the spin accumulation element. However, with the present micro fabrication technique, the magnetic substance interval is about 30 nm at minimum, and impossible to narrow down to infinitesimal. Also, if the magnetic substance interval distance is smaller, a magnetic interaction acts between two magnetic substances, possibly degrading the magnetic characteristics. Therefore, there is a demand for a new method for reducing the attenuation of spin electrons without narrowing down the magnetic substance interval.